(1) Field of the Invention
The present invention relates to blowers used on high efficiency (e.g. 90% or higher efficiency) furnaces for drawing air from outside the home into the furnace to support combustion and for expelling the combustion exhaust products outside the home. More particularly, the invention relates to a construction of a blower housing that maximizes the interior space available for the blower impeller.
(2) Description of the Related Art
Combustion blowers for high efficiency furnaces are common in the art. These blowers are used to draw air for combustion from outside the home. Generally, these blowers are located downstream of a combustion chamber or combustion tubes in the furnace, depending upon the style of furnace, into which the combustion air is drawn, mixed with fuel, and ignited to generate heat for the furnace. The exhaust gases are drawn into the suction side of the blower and discharged from the blower through an exhaust pipe that vents to outside atmosphere.
Although the mounting arrangement and available space inside the blower is similar between one furnace model and the next, each model of furnace typically is designed to use a specific type and size blower. Among other general specifications set by the furnace manufacturer, the blower must meet requirements for dimensional size, mounting arrangements, and air moving capacity. In particular, the size of the blower housing must fit within a given space which then in turn determines the location of mounting holes in the furnace bonnet. Thus, these dimensional size requirements limit the air moving capacity of a blower because the impeller size must be chosen to fit and operate efficiently within the given size housing.
In order to increase the air moving capacity of the blower given the fixed size for the blower housing and the impeller, the designer may choose to increase the speed of the impeller. This in turn requires that the blower be operated with a higher speed motor. This option has significant drawbacks, including increased cost to buy, to operate, and increased noise. The speed of the motor and the speed of the impeller must be closely matched to maximize efficiency of the impeller. This requires additional engineering considerations in designing the impeller to operate efficiently at increased speeds. Efficient high speed motors are generally more expensive and tends to increase the cost of the blower. A blower with a higher speed motor also tends to produce more noise and vibration. The higher speed motor also has greater electrical demands. High speed blower motors tend to operate at higher temperatures and generate more heat than lower speed motors. Since the motor is in close proximity to hot exhaust gases in the blower, higher speed motors may require auxiliary cooling systems such as a shaft mounted fan, or a larger bonnet interior to avoid heat buildup. Auxiliary cooling systems lower motor efficiency, and the higher operating temperatures tend to decrease the life cycle of the blower motor.
FIG. 1 shows a blower 20 of the prior art arranged on a blower mounting surface 21 of a furnace 22. The blower 20 includes a blower motor (not shown) and a blower housing 24. In FIG. 1, the blower motor has been removed from its center mount 26 on top of the blower housing 24 to show greater detail of the blower housing 24. The blower housing 24 has a side wall 28 extending between a top piece 30 and a bottom piece 32. The top piece 30 is molded with the center mount recess 26 to receive the blower motor (not shown). The side wall 28, top piece 30, and bottom piece 32 form a volute 34 for the blower housing 24. When the blower 20 is energized, an impeller (not shown), operably connected to a shaft of the blower motor (not shown), rotates in the volute 34 to draw exhaust gases through an inlet hole 35 in the center of the bottom piece 32 and to compress gases in the volute 34. The pressurized exhaust gases are directed into a discharge pipe 36 that extends outward and away from the blower 20 and the furnace 22.
As shown in FIG. 1, mounting feet 38 for attaching the blower 20 to the blower mounting surface 21 of the furnace 22 are provided on the side wall 28 of the blower housing 24. In order to secure the blower housing 24 to the furnace, mechanical fasteners 40 are used. The typical mechanical fastener 40 used to secure the blower 20 to the furnace 22 has a screw head driving end 42 and an opposite driven end 43 spaced from the driving end 42 by a shaft 44. The driving end 42 is larger than the shaft 44 such that it engages a seating surface 46 on the mounting foot 38 and holds the blower 20 to the furnace. The seating surface 46 of the mounting foot 38 is sized to allow clearance between the driving end 42 of the fastener 40 and the side wall 28 of the blower housing 24.
In the construction of older blower housings, a cut-out in the side wall of the blower housing is sometimes provided adjacent the mounting feet for clearance of the driving end of the mechanical fastener. A sponge foam rubber or rubber type sealing insert is then used once the fastener is installed to completely seal the housing along the narrow spacing adjacent the driving end of the fastener. These inserts and gaskets are problematic in that they tend to leak over time and represent the weak link in exhaust system integrity. Additionally, some blower housing constructions require the use of gasket material to build up the axial height of the bottom piece in the area of the mounting foot when the blower is installed on the furnace. This gasket material seals the blower housing in the area of the mechanical fastener and prevents the mounting foot from heeling over when the mechanical fastener is tightened and the blower housing is attached to the furnace.
What is needed to overcome the disadvantages of the prior art is a blower housing which has a maximized interior space to permit the use of the largest capacity impeller practicable while meeting the size restrictions set by the mounting holes located in the furnace by the manufacturer. The blower housing having the largest practicable capacity impeller would meet the manufacturer""s requirements for air moving capacity with a lower speed motor. Such a blower would meet furnace manufacturers"" specifications for air moving capacity with decreased noise and vibration, and cost for the blower. Additionally, such a blower would eliminate the need for sealing inserts or gasket materials at the mounting locations for the blower housing.
In order to overcome the disadvantages of the prior art, the blower of the present invention provides an increased interior spacing while maintaining fixed exterior dimensions including especially the mounting hole locations. By having a larger interior for containing a larger impeller than in the prior art design, the blower of the present invention is capable of generating a higher air moving capacity with a decreased operating speed, cost, and lower noise and vibration levels. The blower of present invention also improves the containment of exhaust gases in the blower housing by improving the integrity of the seal around the housing against the furnace bonnet.
The blower of the present invention includes a blower housing and a blower motor. The blower housing has a top piece, a side wall, and a bottom piece that detachably engages the top piece to enclose the blower housing. The top piece includes an annular lower support portion for supporting the blower motor and an annular upper portion extending above and around the lower portion. The upper portion of the top piece of the blower housing has an outer peripheral edge and at least one lug extending outwardly beyond its outer peripheral edge. The bottom piece of the blower housing has a flange extending beyond its periphery that aligns with the lug of the top piece when the blower housing is assembled. The flange interlocks with the lug to detachably engage the top piece to the bottom piece. The top piece, side wall and bottom piece thus form a volute for the blower housing when assembled.
The lug on the top piece has a lug hole to receive a mechanical fastener such as a threaded bolt or screw. The flange on the bottom piece preferably has a flange hole that receives the mechanical fastener therethrough when the mechanical fastener joins the top piece to the blower mounting surface of the furnace. The mechanical fastener preferably attaches the blower housing to the furnace such that the blower housing is positioned between a blower motor and exterior mounting surface of the furnace. Thus, by locating the mechanical fastener with its head above the top piece, it may be driven tightly against the lug at the top of the blower and space need not be provided for the head of the mechanical fastener to be driven tightly against a blower housing surface which itself is located within the envelope of the impeller space.
In other words, in the prior art construction as seen in FIG. 1, a seating surface 46 is provided against which the driving end must be snugged to adequately secure the blower to the furnace. This requires a shoulder of a minimum width between the lug hole and the blower housing sidewall, which shoulder width (along with any clearance between the mounting hole sidewall and the shoulder) represents wasted space as the location of the blower housing sidewall is what limits the diameter of the impeller. With the present invention, the blower housing sidewall may be immediately adjacent the shaft 44 as the driving end is snugged against a surface located above the blower housing sidewall. Thus, little clearance need be provided between the shaft as the screwdriver or other tool used to secure the mechanical fastener has complete and unimpeded access to the driving end as it remains above the blower housing.
In another aspect of the present invention, the blower housing is provided with an improved seal between the top and bottom pieces. Preferably, the blower housing comprises a bottom piece having a disk shaped bottom portion with an outer perimeter border and an upstanding annular wall extending outward from the bottom disk around the outer perimeter border. The upstanding annular wall has an interior surface that forms a portion of the volute for the blower housing. The upstanding wall has an annular end axially opposite the bottom disk portion that extends between the exterior and interior surfaces of the upstanding wall. The annular end has an annular lip axially spaced from the annular end.
The top piece fits over the bottom piece to enclose the volute and form a casing for the blower. The top piece has a lower portion recessed into the top piece and extending into the casing. This lower portion receives the blower motor. The top piece also has an upper portion which extends around and above the lower portion. The upper portion has a primary groove and an outer peripheral edge surrounding the primary groove. The primary groove has an annular outer side wall and an annular inner side wall spaced apart by an annular groove wall. The groove wall has a secondary groove intermediate the coterminous edges of the groove wall and inner and outer side walls. The inner side wall of the primary groove abuts the interior surface of the upstanding wall of the bottom piece and the annular lip of the bottom piece is received in the secondary groove when the casing is assembled.
The inner side wall of the primary groove preferably has an annular rib extending outwardly from the side wall into the primary groove. The interior surface of the upstanding annular wall preferably has an annular notch on its interior surface. In this arrangement, as the annular notch receives the annular rib in the primary groove, the pieces tend to xe2x80x9csnapxe2x80x9d together as the bottom piece is fully assembly with the top piece. This construction thus provides a positive indicator of sealing between the top and bottom pieces when the blower housing is assembled.